Electrocardiographic differentiation of early repolarization from subtle anterior ST-segment elevation myocardial
Stephen W Smith1, Ayesha Khalil, Timothy D Henry
1Hennepin County Medical Center, Minneapolis, MN, USA. smith253@umn.edu
Insights
Differentiating subtle anterior ST-segment elevation myocardial infarction (STEMI) from early repolarization using ECG is challenging. A new ECG equation combining R-wave amplitude, ST-segment elevation, and corrected QT interval (QTc) accurately distinguishes between these conditions.
Area of Science:
- Cardiology
- Electrocardiography
Background:
- Anterior ST-segment elevation myocardial infarction (STEMI) can be difficult to distinguish from early repolarization on ECG.
- Accurate differentiation is crucial for timely and appropriate patient management.
Purpose of the Study:
- To identify specific ECG measurements that best differentiate subtle anterior STEMI from early repolarization.
- To develop and validate a predictive ECG criterion for this differentiation.
Main Methods:
- Retrospective analysis of ECGs from patients with anterior STEMI and early repolarization.
- Measurement of ST-segment elevation, T-wave and R-wave amplitudes, and computerized corrected QT interval (QTc).
- Multivariate logistic regression to derive and validate an ECG-based predictive equation.
Main Results:
- Subtle anterior STEMI showed greater ST-segment elevation, lower R-wave amplitude, and longer QTc compared to early repolarization.
- A validated ECG equation incorporating R-wave amplitude (V4), ST-segment elevation (V3), and QTc achieved 88% accuracy in differentiating the two conditions.
- Upward concavity and J-wave notching were not significant differentiating factors.
Conclusions:
- Lower R-wave amplitude, greater ST-segment elevation, and longer QTc are key indicators of subtle anterior STEMI versus early repolarization.
- The derived ECG equation serves as a valuable adjunct for diagnosing anterior STEMI in clinical practice.
Study Objective:
Anterior ST-segment elevation myocardial infarction (STEMI) can be difficult to differentiate from early repolarization on the ECG. We hypothesize that, in addition to ST-segment elevation, T-wave amplitude to R-wave amplitude ratio (T-wave amplitude(avg)/R-wave amplitude(avg)), and R-wave amplitude in leads V2 to V4, computerized corrected QT interval (QTc) and upward concavity would help to differentiate the 2. We seek to determine which ECG measurements best distinguish STEMI versus early repolarization.
Methods:
This was a retrospective study of patients with anterior STEMI (2003 to 2009) and early repolarization (2003 to 2005) at 2 urban hospitals, one of which (Minneapolis Heart Institute) receives 500 STEMI patients per year. We compared the ECGs of nonobvious ("subtle") anterior STEMI with emergency department noncardiac chest pain patients with early repolarization. ST-segment elevation at the J point and 60 ms after the J point, T-wave amplitude, R-wave amplitude, QTc, upward concavity, J-wave notching, and T waves in V1 and V6 were measured. Multivariate logistic regression modeling was used to identify ECG measurements independently predictive of STEMI versus early repolarization in a derivation group and was subsequently validated in a separate group.
Results:
Of 355 anterior STEMIs identified, 143 were nonobvious, or subtle, compared with 171 early repolarization ECGs. ST-segment elevation was greater, R-wave amplitude lower, and T-wave amplitude(avg)/R-wave amplitude(avg) higher in leads V2 to V4 with STEMI versus early repolarization. Computerized QTc was also significantly longer with STEMI versus early repolarization. T-wave amplitude did not differ significantly between the groups, such that the T-wave amplitude(avg)/R-wave amplitude(avg) difference was entirely due to the difference in R-wave amplitude. An ECG criterion based on 3 measurements (R-wave amplitude in lead V4, ST-segment elevation 60 ms after J-point in lead V3, and QTc) was derived and validated for differentiating STEMI versus early repolarization, such that if the value of the equation ([1.196 x ST-segment elevation 60 ms after the J point in lead V3 in mm]+[0.059 x QTc in ms]-[0.326 x R-wave amplitude in lead V4 in mm]) is greater than 23.4 predicted STEMI and if less than or equal to 23.4, it predicted early repolarization in both groups, with overall sensitivity, specificity, and accuracy of 86% (95% confidence interval [CI] 79, 91), 91% (95% CI 85, 95), and 88% (95% CI 84, 92), respectively, with positive likelihood ratio 9.2 (95% CI 8.5 to 10) and negative likelihood ratio 0.1 (95% CI 0.08 to 0.3). Upward concavity, upright T wave in V1 or T wave, in V1 greater than T wave in V6, and J-wave notching did not provide important information.
Conclusion:
R-wave amplitude is lower, ST-segment elevation greater, and QTc longer for subtle anterior STEMI versus early repolarization. In combination with other clinical data, this derived and validated ECG equation could be an important adjunct in the diagnosis of anterior STEMI.
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